The present invention relates generally to testing apparatus, and more specifically to apparatus and methods for applying a biaxial load to a flat test specimen.
Prior art methods for applying a biaxial load to a test specimen require either two or more separate actuators, complex specimen configurations, or pressurization techniques. A common method for creating a biaxial stress state requires a loading apparatus having two orthogonally mounted actuators. A specimen is attached to the two actuators to produce loads along two orthogonal axes. A particular disadvantage of this approach is the high cost of the equipment, which often must be custom made.
A cruciform, or cross-shaped, specimen has also been used in the biaxial stress testing prior art. The orthogonal arms of the cruciform are both put under a tensile load with the central portion of the intersecting region being the test area undergoing a biaxial stress. The disadvantages of this method are that two or more loading devices are required and excess material and fabrication time are required for the specimen compared to a straightforward flat plate.
Another prior art method for biaxial loading is pressurizing the inside surface of a cylindrical specimen and applying compressive loads to the end of the specimen. One disadvantage of this method is that the specimen must be cylindrical, requiring more material and fabricating time than a simple flat plate specimen. Another disadvantage is the high cost of the equipment necessary to pressurize the cylinder.
Thus it is seen that there is a need for a simple, straightforward apparatus and method for applying a biaxial stress to a flat plate test specimen.
It is, therefore, a principal object of the present invention to provide such a simple and straightforward apparatus and method.
It is a feature of the present invention that it is compatible with conventional uniaxial test equipment.
It is an advantage of the present invention that it is inexpensive to make, to use and to fabricate test specimens.
It is another advantage of the present invention that it allows a wide variety of load combinations.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.